There is an ever increasing demand for power conversion and regulation circuitry to operate with increased efficiency. One such type of regulator circuit is known as a switching regulator or switching power supply. A switching power supply controls the flow of power to a load by controlling the “on” and “off” duty-cycle of one or more transistor switches coupled to the load. One such way of controlling the “on” and “off” duty-cycle of the one or more transistor switches is to generate a pulse-width-modulated (PWM) signal, such that the “on” and “off” duty-cycle of the one or more transistor switches is determined by relative pulse-widths of the PWM signal. Switching power supplies have been implemented as an efficient mechanism for providing a regulated output. Many different classes of switching power supplies exist today.
To achieve a regulated output, a switching power supply often generates a current that is switched between a positive supply voltage and ground, such that the generated current is applied to a load. Switching power supplies often include over-current sensing and protection schemes to prevent the switching power supply from being damaged as a result of an over-current condition. Since resistive loads generate power loss in the form of heat, one manner of providing increased efficiency in a switching power supply is to use transistor switches that have a low activation resistance (RDSon). However, transistor switches with a low RDSon value may generate current too quickly as the low RDSon, value substantially creates a short circuit to the positive supply voltage or to ground. As such, typical over-current sensing and protection schemes may not be sufficient to limit the current flow quickly or effectively enough to prevent damage to the switching power supply. In addition, as switching power supplies become more efficient, the on duty-cycle of transistor switches can typically be very small. As there is often a delay associated with current sensing, it may be difficult to measure current flow through a switching transistor that is only activated for a very short period of time. Accordingly, a current sense hole could exist, such that an indeterminable over-current condition could exist in the switching power supply.